''Impidens'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of large omnivorous

cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

from the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

and

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

. Its type and only species is ''Impidens hancoxi''. ''Impidens'' inhabited high-latitude environments of southern

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

during the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

, where it was probably the apex predator.

History

A specimen of ''Impidens'' was collected from Antarctica in 1986. In 1995, it was described as an indeterminate

diademodontid Diademodontidae is an extinct family of Triassic gomphodonts. The best-known genus is ''Diademodon'' from South Africa. ''Titanogomphodon'' from Namibia may also be a member of Diademodontidae. The Chinese genera ''Hazhenia'' and ''Ordosiodon'' ha ...

possibly belonging to '' Titanogomphodon''. The holotype of ''Impidens hancoxi'' was found in South Africa in 2014. It was described as a new species in

2021 File:2021 collage V2.png, From top left, clockwise: the James Webb Space Telescope was launched in 2021; Protesters in Yangon, Myanmar following the 2021 Myanmar coup d'état, coup d'état; A civil demonstration against the October–November 2021 ...

, with the Antarctic specimen and a less complete specimen from South Africa being referred to the species.

Description

''Impidens'' was one of the largest non-mammalian cynodonts, with a skull well over long, though the herbivorous '' Scalenodontoides'' from the Late Triassic was even larger.

Classification

''Impidens'' is a member of

Trirachodontidae Trirachodontidae is an extinct, possibly paraphyletic family of cynognathian cynodonts from the Triassic of China and southern Africa. Trirachodontids appeared during the Early Triassic soon after the Permian-Triassic extinction event and quickl ...

, a family of gomphodont cynodonts. It is closely related to its smaller contemporary ''

Cricodon ''Cricodon'' is an extinct genus of trirachodontid cynodonts that lived during the Early Triassic and Middle Triassic periods of Africa.Abdala, F., J. Neveling, and J. Welman. 2006. A new trirachodontid cynodont from the lower levels of the Burg ...

'' as well as the earlier ''

Langbergia ''Langbergia'' is an extinct genus of trirachodontid cynodont from the Early Triassic of South Africa. The type and only species ''L. modisei'' was named in 2006. ''Langbergia'' was found in the Burgersdorp Formation in the Beaufort Group, a pa ...

'' and '' Trirachodon''. However, the phylogeny of Trirachodontidae is not well-understood, and the family may be paraphyletic, with some species more closely related to

traversodontids Traversodontidae is an extinct family of herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe and eastern North America. ...

than others.

Paleoecology

''Impidens'' fossils are known from the ''Cricodon''-''Ufudocyclops'' subzone of the ''Cynognathus'' Assemblage Zone of the

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underlie ...

in South Africa and the upper

Fremouw Formation The Fremouw Formation is a Triassic-age rock formation in the Transantarctic Mountains of Antarctica. It contains the oldest known fossils of tetrapods from Antarctica, including synapsids, reptiles and amphibians. Fossilized trees have also been ...

in Antarctica. The dating of these strata is controversial; they are conventionally regarded as

in age, probably late

Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic Ep ...

or early

Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic). ...

, but a biostratigraphically correlated fauna in

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

has been dated to the beginning of the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

, in the early

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...

. However, another biostratigraphically correlated fauna in

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

has been dated to the

, suggesting the traditional dating may be correct. ''Impidens'' was probably the apex predator of its environment, as the only other large predator known to have coexisted with it was the somewhat smaller cynodont ''

Cynognathus ''Cynognathus'' is an extinct genus of large-bodied cynodontian therapsids that lived in the Middle Triassic. It is known from a single species, ''Cynognathus crateronotus''. ''Cynognathus'' was a long predator closely related to mammals and ha ...

''. The known large herbivores of the fauna are the cynodont ''

Diademodon ''Diademodon'' is an extinct genus of cynodonts. It was about long. Discovery Harry Seeley had found his fossil in the Burgersdorp Formation of the Beaufort Group in the Karoo Basin of South Africa. As late as 1988, ''Diademodon'' had bee ...

'' and the dicynodont ''

Ufudocyclops ''Ufudocyclops'' is an extinct genus of stahleckeriid dicynodont from the Middle Triassic of South Africa. It was found in the Burgersdorp Formation, part of the uppermost ''Cynognathus'' Assemblage Zone of the Beaufort Group in the Karoo Basin ...

''. A smaller trirachodontid, ''

'', was also present in the environment. The ''Cricodon''-''Ufudocyclops'' subzone was deposited in a meandering river environment, with a deep channel and high banks. Both it and the Fremouw Formation were high-paleolatitude environments, which may explain some of the faunal differences between them and lower-paleolatitude fauna.

Footnotes

References

Bibliography

* * * {{Taxonbar, from=Q108084621 Cynognathians Prehistoric cynodont genera Fossil taxa described in 2021 Middle Triassic synapsids of Africa Triassic Antarctica Fossils of Antarctica Extinct animals of Antarctica Fossils of South Africa